Laminated timber beams are used in a variety of structural and architectural applications, including residential, commercial, and industrial construction applications. The use of glued-laminated timbers (glulam), which are typically comprised of finger-jointed and face-bonded dimension lumber laminations, provides a multitude of advantages over conventional solid wood timbers for such applications. One such advantage is the ability to produce thicker, wider, and longer structural members, since the dimensions of the original lumber source do not limit the size and shape of the glulam laminations. Another such advantage of glulam beams is that by creating a beam of layered solid sawn or composite wood products, individual strength reducing defects are randomized throughout the beam volume, resulting in an increase in the overall strength of the glulam beam.
Wood laminations are typically graded visually based upon knot dimensions, grain angle deviations or other defects. Wood laminations are also graded mechanically to determine the modulus of elasticity as a measure of bending strength and stiffness. The traditional cross-sectional configuration of a glulam beam is comprised of a uniform series of laminations of equal thickness. It is known that the overall structural strength of the beam can be improved by placing higher-grade wood laminations in the compression and tension regions of the beam where the tensile and compressive stresses on the beam are highest. This traditional glulam composition meets or exceeds the strength of the solid timber counterparts, with the added advantage of being an efficient and conservation-conscious use of the wood resource.
In recent years, there has been increasing pressure on the lumber industry based upon the scarcity of the high-grade wood resource. This has made it more difficult and more costly to acquire the high-grade tension laminations needed to maintain competitive strength and stiffness design properties of traditional glulam beams. A recent solution to this problem has been the use of fiber-reinforced polymer panels at the extreme compression layer and the tension layer of the beam. More recently, another approach has been to use laminated veneer lumber (LVL) rather than solid-sawn lumber at the extreme compression and tension layers of the beam. The LVL laminate is a fabricated lamination of wood veneer layers, and functions as a replacement for the high-grade laminations. Such products have served as equivalents from a performance standpoint and address the scarcity of high-grade wood materials. However, these alternative beam designs to the conventional glulam beams are expensive to manufacture and raise consumption issues of alternate scarce resources, such as petroleum. Thus, it would be advantageous to develop a laminated beam that significantly improves glued-laminated timber beam performance, or reduces manufacturing cost, without relying on a large percentage of higher-grade wood laminations or fabricated wood lamination alternatives. Preferably, such a laminated beam would achieve substantially the same or superior performance results achieved by conventional glulam beams.